The present invention is concerned with an independent wheel brake unit for a modular brake system of an automotive vehicle.
Conventional brake systems for automotive vehicles are designed as hydraulic or pneumatic brake systems. Essentially, they are composed of a central actuator which, through supply conduits, communicates with the wheel brakes which are decentrally arranged in the area of the automotive wheels. The energy required for actuating the brake system is made available in the central actuator and, with the aid of supply conduits, is distributed among the wheel brakes. Also, the hydraulic pressure of the wheel brakes is controlled through the supply conduits.
In a simple hydraulic brake system, the actuator, through a brake pedal, is controlled by the driver and at the same time is provided with energy. In more complex brake systems, the control of the wheel brakes is supplemented, for example, by an anti-locking system (ABS) or an automatic slip control (ASR) while the energy supply is supplemented by a brake force booster or a hydraulic pump. Such additional assemblies and systems are disposed centrally and obtain their energy from the engine of the automotive vehicle, in general indirectly, through the electrical wiring system of the automotive vehicle.
However, conventional brake systems of the above-mentioned type require substantial mounting efforts. Requiring substantial mounting efforts is in opposition to the requirements of modern automobile construction, which attempt to reduce final-assembly costs. In addition to the wheel brakes, a plurality of other central units are required to be assembled and interconnected, which substantially contributes to the high cost of assembly. The placement and connection of hydraulic conduits and hoses are particularly costly and susceptible to trouble. Moreover, electrical conduits for data communication, e.g. for the connection of rotary speed sensors on the vehicle wheel to the central ABS-control unit, are required.
A wheel brake unit for automotive vehicles is disclosed by United Kingdom Patent No. 1,359,487. In this system, a hydraulic wheel brake, a hydraulic pump, and control valves, in conjunction with a sensor for determining the rotational speed of the vehicle wheel and with an associated electronic control element, are combined as a unit and mounted on the vehicle wheel. However, the pump alone is not responsible for brake operation, but it operates solely to modulate the hydraulic pressure in the wheel brake. In general, brake operation is performed in a conventional fashion via a hydraulic pressure line which conveys the actuating energy in the form of hydraulic pressure from a central supply unit, e.g. a master brake cylinder, to the wheel brakes. In this respect, this known wheel brake unit does not differ greatly from the arrangements referred to above.
Another disadvantage of conventional brake systems resides in that they obtain their energy from the electrical energy supply system of the automotive vehicle. In modern automobiles, the electrical wiring system is loaded by an increasing number of consumers of electricity. In consequence thereof, the power supply and the network must be modified to accommodate the increased number of consumers, thereby raising the costs of manufacture. Finally, reference should be made to the increasing energy consumption virtually resulting in an increased fuel consumption, which is unacceptable in view of the pollution problems involved therewith.
German patent DE 2,128,169 teaches an electrically-operated brake system. In this system, a wheel brake, in conjunction with electric actuating elements and control elements, is provided as a unit and mounted on the vehicle wheel. However, the electric control of the brake operation is performed from a central point in the vehicle, and the electric energy is supplied from a central point in the vehicle. Also, the electrical wiring system is under stress.